Operations
Tach time
Time recorded by the tachometer, proportional to engine RPM - it runs slower than clock time at low power. The usual basis for maintenance intervals.
In practice
Because the tach counts revolutions rather than minutes, an hour of pattern work might log only 0.8 on the tach while the Hobbs shows 1.0. Maintenance schedules - 100-hours, oil changes, TBO - track tach, so partnerships that bill by tach align what members pay with what the engine actually consumed. The tradeoff is slightly lower revenue per clock hour than Hobbs billing.
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